The invention relates to an apparatus for the section-wise autofrettage of or cold working barrels, particularly gun barrels, by a hydraulic internal pressure that is generated inside the barrel.
During firing, gun barrels are stressed by extremely high gas pressures, which cause the barrel, and thus the inside barrel surface, to expand. To increase the resistance to barrel expansion during firing, it is known to subject the corresponding barrel to an autofrettage. In the process, pressure exerted on the inside surface of the barrel exceeds the elasticity limit of the inside layers, thereby causing a permanent deformation through the expansion of these layers, which press against the outside layers. The permanent deformation is not subjected to further changes during firing, because the high pressure attained in the autofrettage is not reached again.
German patent DE-PS 1 124 987 discloses a method for the autofrettage of gun barrels, in which a hydraulic internal pressure is generated inside the barrel. The pressure decreases continuously with increasing distance from the charge-side barrel end, taking into account the pressure course of the propellant-charge gases in the barrel during firing. To this end, a highly viscous fluid that is under high pressure flows continuously through the annular gap formed between the inside wall of the barrel and a mandrel-shaped metal insert. The width of the annular gap determines the local pressure stress.
It is further known from German Patent No. DE-PS 1 124 987 that it was not possible up to now to perform a satisfactory section-wise autofrettage, because the sealing devices required between the different longitudinal sections were not available.